1. Field of the Invention
This invention most generally relates to an improved gas stove which has two indirect fired burner assemblies. An indirect fired burner is one in which the air for combustion is separated and not mixed with the convection air used for transferring heat to the food being cooked/broiled/baked. There may be multiple burner tubes or heat source devices associated with each burner assembly. The stove may have a capability to generate steam within the oven cavity of the gas stove or external to the cavity and ducted into the cooking space. The stove may also have a capability to be pyrolytically self-cleaning. The improvements speed the cooking time and results in the cooked food having retained a substantial amount of the flavor of the food prior to cooking. The improvement of the flavor of the resulting cooked food is a result, at least in part, of the control of the convection/cooking air, and/or by the introduction of steam into the oven cavity.
This invention more generally relates to gas stoves having two indirect fired burner assemblies, a bake and broil oven and an optional steam cooking capability. The optional steam cooking capability is possible due at least in part to the separation of the combustion gases from the air used to heat the food products--the convection air. The combustion gases are kept separate, in part through the use of a heat exchange and appropriate ducts, from the convection air used in the baking mode. The gases from the radiant heat source, the broiler assembly, are kept separate from the oven space, in part through the, use of a radian heat transfer apparatus which transfers radiant energy which maintaining the integrity of the oven volume. The gas stoves may be used either commercially and/or in the home and may be self-cleaning and have a broiling capability. More particularly the invention relates to a new indirect fired two burner assembly gas burning device such as a counter-top oven or a full sized oven which is capable of the functions of conventional and convection bake, broil, steaming, including programmable combinations of these various modes, and which may have a pyrolytic self-clean function. In the broil mode the radiant heat to the broiled products is indirect radiant heat in that the flame of the broil burner assembly does not "see" the broiling products. Further and preferably, a recirculation air blower may be variable in speed to control the baking regimen. There is thus provided a variable convection flow which permits high convection air flow rates for roasting and the like and permits low flow rates (conventional-like baking) for preparing more delicate baked products.
2. Description of the Prior Art
There are basically two approaches used to create the common gas oven configurations, the single cavity for bake and broil and an oven which features a large bake cavity and a smaller drawer for broiling. The single cavity designs use two separate burners to achieve bake and broil conditions whereas the two compartment approach shares a common burner.
To achieve bake conditions the single oven utilizes a gas burner subassembly located under the floor of the oven. The hot products of combustion flow through openings in the oven floor and heat the oven surfaces and interior space. This method of heating prevents the baked goods from looking directly at the burner. Broiling is accomplished by exposing the top surface of the food product directly to a highly radiant burner subassembly.
In a single oven approach, a separate broil burner is mounted at the top of the oven cavity looking directly down on the oven space. Typical broil burners are radiant screen or blue flame burner where the flame rolls over a metal spreader. With either approach, the burner looks directly at the food imparting a high radiant heat flux to the product. A single oven cavity approach is the typical configuration used for obtaining pyrolytic cleaning or self-cleaning oven performance. This cleaning process occurs when the soiled surfaces of the oven cavity reach temperatures in excess of 800.degree. F. which usually corresponds to oven air temperatures in the range of 875.degree. F. to 925.degree. F. Maintaining this high temperature condition for an extended period of time will result in the reduction of food soils to a powdery ash residue. This cleaning process is most effective except in the regions of the door gasket where the short conduction paths to the cooler door result in somewhat cooler surfaces with resulting reduction in cleaning performance.
This single cavity gas range is a relatively recent advancement in oven design. In the older design, the oven is configured with a large baking oven cavity and a lower smaller broiler cavity. A single burner is mounted between the two cavities and this burner looks directly into the broiler drawer for the desired radiant heat energy input to the food. During bake the hot gases produced by the single burner flow through the oven floor into the bake cavity. This oven design is not typically or readily adapted or adaptable for self-cleaning temperatures.
U.S. Pat. No. 3,973,551 to Caselini et al discloses an arrangement which is substantially different from the subject invention in that it uses a single bottom burner combined with a recirculating fan or blower for circulating hot air throughout the oven. While the specification indicated that the oven can direct substantial heat from the top area, it is not specifically seen to disclose a capacity for broiling in the conventional sense.
German AS 1 241 080 is of interest as regards the disclosed invention in that it illustrates the use of a single top burner and a recirculating fan for heating an enclosed oven cavity. However, hot gases are not circulated through the oven, but rather around the oven cavity. Thus, there is not observed a broiling capacity and the overall arrangement is substantially different from the subject invention.
U.S. Pat. No. 3,659,579 to Henderson et al shows an oven capable of baking and broiling, as well as self-cleaning. A single burner at the top of the oven is utilized as both a broiling and baking burner, with a recirculating fan arranged to move hot air and products of combustion throughout the oven space. It is to be noted that both broiling and baking heat are supplied from the top of the oven, with the burner having a two-position configuration for broiling or baking. The overall arrangement of the burner and recirculating fan are seen to be considerably different from that used the subject invention as disclosed herein by Applicant.
U.S. Pat. No. 3,437,085 to Perry shows a single top burner arrangement for an oven that can bake, broil or self-clean. However, there is not seen to be disclosed in this patent any arrangement comparable to the recirculating/diverting fan arrangement used in the subject invention.
The patents to Herrelko et al U.S. Pat. Nos. 4,598,691, Henderson et al 3,659,579, Day 4,373,504 and Miller 4,700,685 describe systems which are very different from the present invention. They all disclose single burner elements, no separation of the combustion air and the convection air, no heat exchanger device and only a single fan or blower except for the patent to Day who does disclose two blowers. Additionally, except for the patent to Miller steam cooking is not disclosed. The patent to Ishii et al U.S. Pat. No. 4,648,381 does disclose two burners and also means for steam generation. However, again there is a single fan, but no heat exchanger, and no provision for the separation of the combustion and the convection or baking air.
It would be advantageous to provide an indirect gas fired oven having two burner assemblies which would operate in the broil, bake, steam and self-clean modes all done in one oven cavity. It would be of additional advantage if the amount of oven/convection air used for baking could be increased and/or controlled. The combustion air and the oven air or convection air being kept separate and the single oven being substantially sealed (tight and thus having a very low vent rate) from ambient air, allows for the economical introduction of steam into the oven cavity.